The Destroyer ran as the cover feature of Mystic #6 and of the remaining four issues of that 10-issue superhero anthology, and while less popular than the company's Captain America, the Human Torch, and the Sub-Mariner, he went on to star in issues of nearly every Timely superhero comic-book series — becoming the company's most-published character outside of those three stars and the Angel.

Americanjournalist Keen Marlow is captured for spying while reporting behind-the-lines in NaziGermany. While imprisoned in a concentration camp—that specific phrase being used before its association with the Holocaust—Marlow is given a super-soldier serum, similar to that given to Captain America, by fellow prisoner Professor Eric Schmitt, an anti-Nazi German scientist. Responding to the chemical (and without the beneficial "Vita-Rays" used to chemically stabilize Captain America's serum), Marlow becomes a prime human specimen who escapes, dons a sleek, dark costume with a skull motif and a skintight blue mask that made him appear inhuman, and adopts a fearsome identity with which he fights the Nazis on their own turf. He was occasionally abetted by an Allied agent named Florence von Banger. Antagonists included the Scar, Herr Sin and Von Maus.

In the Destroyer's retcon appearances in the 1970s, the same origin is recounted except for his identity. Now he is Brian Falsworth, brother of Spitfire (a member of the World War II superhero group the Invaders) and son of James Montgomery Falsworth, Lord Falsworth, who had been the World War I hero Union Jack. In this storyline, when Captain America asked if the Destroyer is or is not "an American named Keen Marlow," Falsworth declined to respond.

Brian Falsworth gave up the Destroyer identity in order to become the new Union Jack, and his friend Roger Aubrey (initially introduced as the superhero Dyna-Mite, a member of the team the Crusaders[5]) became the new Destroyer. Falsworth's story is recounted in passing in Ed Brubaker's 2009–2010 miniseries The Marvels Project as part of the Angel's diary of the war. This retelling claims that "Keen Marlow" was an alias used by Falsworth to enter Germany to spy; he was betrayed and captured, and then empowered well after Captain America.[6] However, prior established continuity showed that Falsworth entered Germany under his real name pre-war to promote appeasement, that he was captured trying to leave Germany shortly after Poland was invaded, and empowered only days later, more than a year before Steve Rogers became Captain America.[7]

Editions of the Official Handbook of the Marvel Universe have since clarified that all three versions of the Destroyer—Marlow, Falsworth, and Aubrey—were active during World War II, with Marlow allowing Falsworth and then Aubrey to simultaneously use the Destroyer identity so as to tactically confuse the Axis. Marlow's post-1940s fate remains a mystery.[8]

Versions of the Destroyer, both in continuity and out, have appeared in various Marvel comics. The Age of the Sentry #5 (March 2009) depicts the character as a member of the Guardians of the Galaxy. The character also made a guest appearance in a 2000s issue of New Invaders.

Marvel's MAXimprint published the five-issue miniseriesThe Destroyer vol. 4 (June-Oct. 2009).[9] Written by Robert Kirkman and drawn by Cory Walker, it starred a version of the character Keene Marlow depicted, according to Kirkman, under "the assumption that he's had an ongoing series since the '40s, so I'm basically writing 'issues #701-#705' ..."[10] In this series, a still-active but elderly Marlowe discovers he has a limited amount of time before he will suffer a fatal heart attack, and sets out to kill his old enemies and anyone else who might threaten his wife, who has a bionic arm, or their grown daughter.[11]

Keene Marlow (his first name slightly different from the earlier comics' "Keen") is enhanced by a super-soldier serum variant, similar to the one used to create Captain America (Steve Rogers), but lacking the Vita-Ray treatment.

Destroyer (second from the left) along with the other five "Forgotten Warriors" as seen in Spider-Man.

The Destroyer appears in the five-Part Spider-Man episode "Six Forgotten Warriors", voiced by Roy Dotrice. Here named Keene Marlowe, he is shown as an old colleague of Captain America and an old friend of Ben Parker, now past his prime with his powers fading. He was one of five people (alongside Whizzer, Miss America, Black Marvel, and Thunderer) who had been given powers in an attempt to duplicate the serum that gave Captain America his powers. After Captain America "sacrificed" his life to stop Red Skull from activating the doomsday device, Destroyer and the others claimed the keys and retired. After his wife had been fatally shot by a bank robber Marlow was attempting to capture, Marlow retired his superhero identity and joined the international espionage agency S.H.I.E.L.D., eventually becoming a high-ranking agent. When Kingpin's Insidious Six were targeting the other teammates of Captain America for the keys, Keen ended up coming out of retirement to help Spider-Man when Doctor Octopus and Shocker raid Aunt May's house for one of the keys.

^Per The Unofficial Handbook of Marvel Comics Creators, volumes one to three star an unrelated, non-Marvel character adapted from The Destroyer series of crime novels: The Destroyer (1989-1990), The Destroyer vol. 2 (1991) and The Destroyer vol. 3 (1991-1992)